In recent years microcomputer equipment such as personal, desk top or lap top computers have become extremely popular for a wide range of business, educational and recreational uses. Such computers typically include a main central processor having one or more memory storage disks for the storage of data. The storage disk or disks are commonly provided as part of a so-called Winchester disk drive unit, sometimes referred to as a "hard" disk. Hard disk systems typically consist of one or more disks which are mounted and rotated by a common spindle. Each disk contains a plurality of narrow, closely spaced concentric tracks wherein serial data can be magnetically recorded for later recovery by a transducer positioned with respect to the desired track. Hard disk drives contain a transducer that magnetizes and senses the magnetic field of a rotating disk. The transducer is integrated into a slider that is typically gimbal mounted to a load beam that is cantilevered from an actuator. The load beam is pivoted by a voice coil motor which moves the slider radially across the surface of the magnetic disk from one data track to another. During operation the rotation of the magnetic disk causes the transducer to be aerodynamically lifted above the surface of the recording medium by an air bearing. This aerodynamic lifting phenomena results from the flow of air produced by the rotating magnetic disk. It is this air flow which causes the slider to "fly" above the disk surface.
During the development and post-manufacture processing of sliders and magnetic storage disks, a variety of tests are generally performed on the devices. For example, to ensure that the slider load beam assemblies comply with manufacturing tolerances, the flying height of a slider assembly is tested before installation into a disk drive. The surface of the magnetic storage disks are also routinely tested for defects. Tests to determine the wear resistance and durability of the slider air bearing surfaces and disk surfaces are also useful. In any event, the testing of either the slider or disk generally requires the periodic loading and unloading of a slider air bearing surface onto a surface of a substrate, such as a rotating magnetic disk.
FIG. 1 illustrates a typical magnetic recording head suspension assembly 100. The suspension assembly 100 includes a flexible load beam 104 that is attached to a slider 102 via a flexible gimbal device 105 at one end and a baseplate 106 at the other end. Baseplate 106 in turn is connected to an actuator, test loader, or other movement mechanism. Raised load rails 110 are provided along opposite sides of load beam 104. The load rails extend substantially perpendicular from the load beam and function as a stiffening member. Load beam 104 is generally bent towards the surface of a rotating magnetic disk 114 at a bend zone 112. Although bend zone 112 is shown located adjacent baseplate 106, it may also be placed along the central portion of the load beam nearer slider 102. The bend in the flexible load beam 104 provides a gram load force to slider 102 which opposes the aerodynamic lift force generated by the rotating disk 114. The resultant of the two opposing forces determines the flying height of the slider relative to the disk surface.
In order to minimize the disk-to-disk spacing in magnetic disk drives, the magnetic head slider suspension assemblies must have a low profile. The suspension assembly profile height is known as the "z-height." As shown in FIG. 1, the z-height 108 is the distance between the air bearing surface 103 of slider 102 and the mounting surface 109 of baseplate 106. In the past, heights in the range of 75 to 100 mils were common. However, as the packing density of disks within memory storage devices has increased, the z-height of the head slider suspension assemblies have accordingly diminished. Today, slider suspension assemblies having z-heights in the range of 20 to 30 mils are common.
As previously discussed, the testing of either the slider or disk generally requires the periodic loading and unloading of the slider onto the surface of a rotating disk. FIG. 2 illustrates a prior art test loader assembly 120 that is used to load and unload a slider 122 onto the surface of a disk 140. The slider suspension assembly 121 includes a slider 122 that is gimbal mounted to a load beam 124. A pair of raised rails 128 are positioned along both sides of load beam 124. Load beam 124 also includes a bend zone 125 located adjacent the load beam baseplate 126. The slider suspension assembly 121 is connected to a stationary mounting block 130 at baseplate 126. A lifter/bail assembly 133 having a lifting tab 136 extending from the end of a pivoting arm 134 is used to raise and lower slider 122 in proximity to disk surface 140. In operation, slider 122 is positioned onto disk surface 140 by pivoting lifter assembly 133 in a clockwise direction about an axis of rotation 137 that is parallel to disk surface 140. The clockwise rotation of lifter assembly 133 causes the preloaded load beam 124 to pivot towards the disk surface at bend zone 125. The subsequent removal of slider 122 from disk 140 is achieved by rotating the lifter assembly 133 about axis 137 in a counter-clockwise direction. It is important to note that lifting tab 136 should not make contact with the surface of the disk during the loading or unloading sequence. Such contact could result in damage to the surface of the disk and cause misalignment of the slider suspension assembly.
Low z-height slider suspension assemblies used in modern high density disk drives typically provide a clearance of approximately 8 mils between the load beam rails 128 and disk surface 140. Since the thickness of lifting tab 136 is approximately 4 mils, a clearance of approximately 2 mils is provided between each of the top and bottom surfaces of lifting tab 136 as it is positioned between the slider load rails 128 and disk surface 140. As a result, tolerances of about 0.5 mils are needed when setting the lifter assembly 133 position in relation to the slider suspension assembly. Such low tolerances make it difficult to properly align the lifter assembly. Moreover, the low tolerances reduce the robustness of the test apparatus. Another problem associated with the use of lifter assembly 133 to position slider 122 is that the repeated engagement and disengagement of lifting tab 136 with load beam 124 effectively reduces the flexibility of the load beam over time. Consequently, the gram load force provided by the load beam will diminish over time creating unwanted variations in test data.
Other prior art methods use a mechanical blade in lieu of a lifter/bail assembly to engage the load beam to position the slider away from the disk. Like the lifter/bail assembly discussed above, the mechanical blade apparatus results in a change of gram load force which makes it difficult to calibrate the test device
Turning now to FIG. 3, a side view of another prior art test loader assembly 150 is shown that is used for loading and unloading a slider 152 onto a disk surface 161. Test loader 150 includes a slider suspension assembly 151. Suspension assembly 151 generally includes a flexible load beam 154 that is attached to a rotating mounting block 158 by a baseplate 156 disposed at one end of the load arm. Slider 152 is typically gimbal mounted to a load beam 154 at an end opposite baseplate 156. In addition, load beam 154 includes a bend zone 155 located adjacent load beam baseplate 156 and a pair of load rails 157 located along both sides of the load arm. Slider 152 is rotated toward and away from disk surface 160 by the rotational movement of mounting block 158 about a single axis of rotation at pivot 162. As illustrated, the distance 170 between the axis of rotation and slider is relatively large. Distance 170 varies, but is generally in the range of approximately 2 to 3 inches. The location of the slider's axis of rotation directly affects the angular position of the slider as it contacts the disk surface 160. More specifically, as the distance between the axis of rotation and the load beam bend zone 155 increases the contact angle between the slider and disk surface also increases. Conversely, as the distance between the axis of rotation and bend zone 155 decreases, the contact angle between the slider and disk surface also decreases. (Note that the portion of the load beam located between bend zone 155 and slider 152 is generally parallel to the slider air bearing surface when the slider is in a fully loaded position. Hence, the location of the axis of rotation in relation to the bend zone of load beam 154 is important.) FIG. 4 illustrates an enlarged view of slider 152 as the slider contacts the disk surface 161 of a disk 160. The contact angle, phi, is defined by the angle between a first plane 180 that is perpendicular to the slider air bearing surface 153, and a second plane 190 that is perpendicular to the disk surface 161.
It is desired to minimize the contact angle between the slider air bearing surface and disk surface. Ideally, the slider air bearing surface 153 and disk surface 161 should be parallel at the moment of contact. As the contact angle between the two surfaces increases, several problems arise. First, the likelihood of contacting an edge of the slider with the surface of the disk is increased. Such contact may scratch, or otherwise damage the disk's surface. In addition, as the contact angle increases the lateral movement of the slider across the surface of the disk also increases during the loading and unloading of the slider onto the disk surface. As shown in FIG. 4, slider 152 moves laterally across the disk surface 161 as it transverses from an initial contact angle to a zero contact angle at a fully loaded position. The lateral movement "A" of the slider across the disk surface is undesirable since it increases the wear of both the slider air bearing surface and the disk surface. Lateral movement of the slider is especially problematic when the slider is loaded onto a stationary disk.
What is needed then is a test loader that solves the aforementioned problems. As will be seen, the present invention provides a method and apparatus for loading and unloading a slider onto the surface of a substrate while eliminating the gram load loss problem associated with prior art test loaders. Further, the present invention provides a method and apparatus that minimizes the lateral movement of the slider along the disk surface as the slider is loaded and unloaded onto the disk surface. The present invention also minimizes the initial contact angle between a slider air bearing surface and the surface of a disk as the slider is loaded and unloaded onto the disk surface.